Terho Kololuoma

Lithographic patterning of benzoylacetone modified SnO2 and SnO2:Sb thin films

Abstract The synthesis of directly UV-photopatternable pure and antimony-doped organo-tin materials is presented. UV-photopatternability has been achieved by using the synthesized benzoylacetone modified tin and antimony 2-isopropoxyethoxides. Photopatterned pure and antimony-doped organo-tin films are crystallized by thermal annealing in order to obtain conductive SnO2 and Sb:SnO2 thin films. The molar ratio between benzoylacetone and metal alkoxides has to be 2 in order to obtain crack-free, good-quality structures. The effects of UV-irradiation, increasing antimony doping level and benzoylacetone concentration on the electrical properties of the single-layered films are analyzed. The highest obtained conductivity was 20 S/cm. Benzoylacetone concentration and UV-irradiation has only a negligible effect on the film electrical conductivities.

UV light induced surface expansion phenomenon of hybrid glass thin films

Liquid-phase deposition of sol-gel method derived hybrid glass materials is utilized for fabrication of UV-light-sensitive thin films. The hybrid glass material undergoes a surface-relief deformation when exposed to UV light. The observed deformation phenomenon is in the form of a physical expansion of the exposed areas. The UV light induced surface expansion of the hybrid glass film was used to fabricate near-sinusoidal diffraction gratings with periods of 24 microm, 18 microm, 12 microm, and 9 microm. The maximum deformation when the material was patterned as a diffraction grating was 0.685 microm. The hybrid glass material features an index of refraction of 1.52 at 632.8 microm, rms surface roughness of 2.2 +/- 0.8 microm after processing, and extinction coefficients of 1.2 x 10-3 microm-1 and 0.47 x 10-3 mm-1 at wavelengths of 633 nm and 1550 nm, respectively.

Combinatorial methods in sol-gel technology

Sol-gel processing consists several variable parameters during materials synthesis and post processing steps. The sol-gel synthesis is rather sensitive for the parameters such as pH, temperature, type of catalyst, reaction time etc. However, this sensitivity can be taken as an advantage when developing and studying new materials and their properties. Furthermore, since the sol-gel technology mainly describes the fabrication of solid state materials from a liquid phase by applying metal alkoxides or metal salts as precursors, the post processing such as sintering has critical effects on the final form and properties of the solid material. Combinatorial chemistry and methods are valuable tools to estimate the effects of different variables and to build-up combinatorial libraries for the sol-gel technique. This paper generally describes potentials and the usage motivation of combinatorial chemistry in the sol-gel technology by taking into account some major steps in the synthesis and processing which are valuable for the estimation of the final product properties. Different kind of post processing steps in the combinatorial manner are studied in details. As an example the post processing of sol-gel derived semiconductor oxides and photosensitivity of hybrid sol-gel glasses are presented. The combinatorial treatment and measurement methods for these materials are explained.

Novel synthesis route to conductive antimony-doped tin dioxide and micro-fabrication method

Abstract A novel method for the fabrication of directly photopatternable pure and antimony-doped organo tin polymers via free-radical polymerization is presented. With all synthesized materials, 3 μm feature sizes can be photopatterned by using a mercury I-line UV-lamp. Photopolymerized organo tin films are crystallized by thermal annealing to obtain conductive pure or antimony-doped tin dioxide thin films. The results indicate that the direct photopatterning process increases the conductivity of fabricated films with all Sb-doping concentrations in comparison with the films fabricated without direct photopatterning. The smallest obtained resistivity for the single layer structure was 0.08 Ω cm.

Concept for zero-alignment micro-optical systems

In this paper we present the results of the first fabrication and micro-assembly experiments of a silicon- wafer based micro-optical table (MOT). Based on these experiments, estimates of position accuracy are reported. We also report on progress in fabrication of lens elements in a hybrid sol-gel material (HSGM). Diffractive optical elements have been patterned in a 13-micron thick HSGM layer on a 150-micron thick soda-lime glass substrate. The measured rms surface roughness was 20 nm. Finally, we describe modeling of MOT systems using non-sequential ray tracing.

Fabrication and characterization of hybrid-glass-based axicons

We introduce a process for applying directly UV photopattern- able materials and processing methods for the fabrication of binary dif- fractive optical elements. We design and model a binary axicon—an optical element that produces an almost diffraction free beam at a speci- fied distance from the element. We also synthesize sol-gel-based hybrid glass materials and tailor their processing parameters to fit to the de- mands of the axicon design. A grating periodicity of 2 mm, an 850-nm structure depth, and certain morphological properties are required to meet the design parameters. The materials are synthesized using zirco- nium(IV)isopropoxide, methacrylic acid and methacryloxypropyltri- methoxysilane as deposition material precursors. We determine the mor- phological and shape characteristics of the fabricated axicons as a function of the lithographic exposure parameters. The optical character- istics of the axicons are measured in terms of the axial and radial inten- sity profiles. The difference between the modeled and measured results is explained.

Transparent conductive sol-gel thin films for photonic applications

Antimony doped tin dioxide (SnO2:Sb) thin films are fabricated by a new simplified sol-gel process. Films are prepared from an alcoholic solution of SnCl4(DOT)4H2O doped with SbCl3. Films are deposited by the spin coating process on sodalime glass, borosilicate glass, silicon wafers and ceramic alumina substrates. The chemical reactions during the heat treatment are monitored by DSC and TG. The chemical composition of the coatings are determined by scanning electron microscopy (SEM). Sheet resistance, Rs, is measured using a linear four-probe technique. Optical properties of the films are also determined. The resistivity of the thin films are presented as a function of the antimony doping level. The smallest sheet resistance of 200 (Omega) /

New method to fabricate 3D optical structures into glass-ceramic films

DAL is found for a 250 nm thick coating on a borosilicate substrate. It is observed that the sheet resistance does not decrease linearly with increasing film thickness. Fabrication possibilities of these materials for the integrated optics based sensors including patterning methods are discussed.

Plastic integrated optoelectronics

Liquid phase deposition of sol-gel method derived hybrid glass materials is utilized for fabrication of UV light deformable thin films. The hybrid glass material undergoes a surface-relief deformation when exposed to UV light. The observed deformation phenomenon is in the form of a physical expansion of the exposed areas. The maximum deformation when the material was patterned as a sinusoidal grating was 643 nm. The hybrid glass material features an index of refraction of 1.52, rms surface roughness of 2.25 +/- 0.83 nm after processing, and extinction coefficients of 1.2 10-3 micrometers -1 and 0.47 10-3 micrometers -1 at wavelengths of 633 nm and 1550 nm, respectively.

Optical and optomechanical structures in hybrid sol-gel materials for use in micro-optical systems

Advances in polymer and sol-gel derived hybrid materials have made possible to integrate optical structures including waveguides, sensors and structures used in passive alignment of optical devices on various type of substrates. Particular attention has been given to the fabrication of electro-optical printed circuit boards (EOPCB). Fundamental problems related to printed circuit boards (PCB) are the insufficient surface smoothness of common PCB substrate (FR4) and different coefficients of thermal expansion between the optical material and substrate. In order to resolve these problems sol-gel hybrid materials and cost effective spray-coating method are employed for the fabrication of optical structures on PCB. Surface roughness of the PCBs can be greatly reduced using additional layer under optical core material. This additional layer behaves also as an optical under-cladding layer. Optical properties of these used materials are determined and optical structures fabricated using these directly photopatternable materials are demonstrated.